The formation of powder forged precision components is well known in the art. This formation process involves compacting a powdered metal into a briquette or other form, sintering the powdered metal briquette to form a preform or blank, and then forging the blank or preform such that a part is formed with the desired shape and dimensions. After the sintering step, the preform is typically transferred directly from the sintering furnace to the forging press without any intermediary cooling. Alternatively, it is also known that the preform can be allowed to cool and then be re-heated by HF induction or other means, prior to the forging process. Whether the preform is transferred directly from the sintering furnace to be formed or is allowed to cool and then is reheated prior to forging, the heated preform or blank is placed into a forging press and then hammered or otherwise formed into the desired part having the proper size and shape.
The as-forged surface produced by conventional powdered metal forging has surface finish, porosity, and oxide characteristics which are dependant on many factors such as preform shape, die lubrication, preform temperature, tooling temperature, and forging tonnage. Typically, the resultant as-forged surface finish and porosity of the preforms manufactured by these prior processes have an optimization limit depending upon these process characteristics.
One application for these preforms or blanks that are formed by these prior processes is the formation of a cam for an inner or outer race of a one-way roller clutch. The surface finish, porosity, and surface oxides of these products, influence the tendency of the cam surface to spalling or other failure. Once the cam surface spalls or otherwise fails, the clutch becomes inoperable and must be replaced. Because the cams of one-way clutch races for roller clutches are more susceptible to spalling at higher loads, sprag clutches are typically used in applications requiring a one-way clutch. Sprag clutches, however, are far more expensive to manufacture than roller clutches.